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This question got me thinking about this.

I know that we measure the Earth's surface temperature by satellite (perhaps somewhat inaccurately, but it's done all the same). Using Venus as an example, can we see see evidence of Venus' 800 degree surface from space or is Venus' temperature deduced more by modeling and the Russian ship that landed there.

All things with heat give off a thermal signature and that signature isn't a single wavelength but a range of wavelength. I assume, by measuring the overall color emitted and/or the peak wavelength, it's a fairly straight forward calculation to work out the temperature.

But when you have an atmosphere, and this is the main part of of my question. I assume, an atmosphere is to some degree transparent, so you'd be seeing in a sense, heat through a medium and inside as well as on the upper surface. But the heat you see diminishes depending on how opaque/transparent that atmosphere is to the specific wavelength.

Are there any good ballpark estimates to how thick (or how dense or pressurized), we can see temperature signatures through an atmosphere? In the case of Venus, does any of it's 800 degree surface temperature generated IR make it through it's atmosphere, where it would be observable by spacecraft, giving a good measurement of it's surface temperature, or was it's surface temperature deduced by different types of models and that mistreated Soviet spacecraft that didn't last long once it had landed.

I imagine some atmospheric gases are more transparent than others.

Just to clarify - a specific "yes/no we can detect IR from Venus' surface" and a more general answer as to how far we can see heat through an atmosphere, are both fine.

Carl Witthoft
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userLTK
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  • This is rather broad, since "IR camera" could mean anything from about 800 nm to 50 microns. Further, atmospheric transmission depends on the composition of said atmosphere. Venus, Mars, and Terra have rather different compositions :-) . – Carl Witthoft Apr 21 '17 at 14:03

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Yes. A thermal image from the surface can be detected, even by amateurs.

The ground is heated to about 700K, and thermal emission at a wavelength of 1 micron is just about observable by skilled amateurs, with the right equipment. Mountains, which are cooler by about 30K, can be seen at this wavelength

From orbit, more details can be seen. Akatsuki used the 1 micron band to observe the surface in 2015

At other wavelengths, cloud patterns are revealed. Galileo took images at 2.3 microns during its flyby. They show sulphuric acid clouds at 50km above the surface (10km below the visible cloud layer) and at about 270K, with gaps exposing the lower atmosphere, glowing at 500K.

James K
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